Apparatus for burning fuel



May 19, 1942. F. D. I- IOFFMAN Q ,5

' APPARATUS FOR BURNING FUEL Filed July 21, 1958 2 Sheets-Sheet 1 INVENT OR. FRED D. HOFFMAN ATTORNEY.

May 19, 1942.

F. D. HOFFMAN APPARATUS FOR BURNING FUEL Filed July 21, 1938 2 Sheets-Sheet 2 INVENTOR. FRED D. HOFFMAN ATTORNEY.

Patented May 19, 1942 UNHTED. STAT APPARATUS FOR BURNING FUEL Fred D. Hofiman, Cleveland, Ohio, assignor of one-half to James T. Shipman, Twinsburg,

Ohio

Application July 21, 1938, Serial No. 220,525

7 Claims.

This invention relates to an apparatus for burning carbonaceous fuels.

One of the principal objects of the present invention is to cause more efiicient combustion of fuel in obtaining heat therefrom.

A correlative object is to admit air into the combustion chamber of a furnace in such a relation to the fuel bed in such furnace that sufficient preheated air is provided for rapid combustion of the evolved gases without appreciably changing the rate of evolution of the gases.

More specific objects are to improve combustion efficiency of a furnace as by admitting preheated air in controlled volume into the combustion chamber over the upper surface of the fuel bed, concurrently with the admission of air to regions throughout the fuel bed and discharging the preheated air so admitted outwardly from the point of admission in close overlying relation to the entire surface of the fuel bed.

The objects mentioned above are attained in part by admitting preheated tertiary air into the combustion chamber of a furnace adjacent the radiating hood thereof, so as to assure more nearly complete combustion ,of all of the evolved gases at such a location that the heat is more effectively applied to the hood.

Another object is to provide a simple and inexpensive device for this purpose and which is so arranged that it may be readily installed in commonly used types of domestic coal burning furnaces without alteration of the furnace structure.

Other objects and advantages will become apparent from the following specification wherein reference is made to the drawings, in which:

Fig. 1 is a side elevation of a domestic coal burning furnace with an apparatus embodying features of the present invention installed, part of the furnace housing being broken away for clearness in illustration;

Fig. 2 is an enlarged central vertical sectional view of the apparatus and part of the furnace illustrated in Fig. 1;

Fig. 3 is a cross sectional view taken on a ,plane indicated by the line 33 of Fig. 2;

Fig. 4 is a cross sectional view taken on a plane indicated by the line 44 of Fig. 2;

Fig. 5 is an enlarged partial vertical sectional view of the cooperating locking elements of the 4 'For the purposes of illustration, the'present invention will be described in connection with a domestic coal burning hot air furnace; its use and application to furnaces of other different types and other combustion equipment, being readily apparent from the illustration and description thereof. Referring to Fig. 1, the'furnace may comprise an outer housing I having discharge pipes 2 for conveying hot air to desired-points of application. Within the housin is the furnace proper which comprises a combustion chamber 3 surrounded by a communicating heat-radiating hood 4 and spanned at the bottom by grate bars 5. mitted through a damper G into the ash pit 'l and thence into the combustion chamber through the fuel bed, as is usual, for maintaining combustion. The furnace is provided with the usual firing passage8 and clean-out passage 9,,the clean-out passage 9 leading into the radiating hood 4. The products of combustion are dis,- charged from the furnace through the usual flue i 9 connected to the radiating hood 4.

The present apparatus can be arranged to extend from the outside of the outer housing I through the clean-out passage 9 into the radiating hood 4 and thence downwardly into overhanging relation to the fuel bed in the combustion chamber 3.

Preferably the apparatus includes an air duct 29 which extends from the inlet of the fuel cleanout passage 9 inwardly through the fuel cleanout passage to the horizontal mid-portion of the combustion chamber 3. the air duct 20 there is provided a depending hollow pre-heating bell 2| which, at its upper end, is connected for communication with theduct 20 and which, at its lower end; has an outwardly flaring discharge'nozzle, to be described later. The. air duct 20 has a portion 24 which is preferably arranged to fit snugly within the entrance to the clean-out passage 9. Projections 25 on the under side of the duct.

20 serve as legs to support'the duct on the lower wall of the clean-out passage. The legs maintain the duct in spaced relation to the bottom wall of the clean-out passage 9 and radiating hood 4 so that heat applied to the duct 20 is not dissipated through the outer radiating walls 7 of the furnace structure.

Within the duct 20 is a partition wall 26 which divides the duct into two conduits, preferably Air may be ad-' On the inner end of of the air entering the enlarged inlet portion 24 can pass beneath the wall 26. At its inner end the wall 26 has a downwardly curved portion 29 so arranged as to direct the incoming air downwardly. The upper wall of the duct 20 is divided into a plurality of portions 39 which are inclined upwardly from the duct axis and outwardly toward the clean-out entrance in staggered relationship so that the outer end of each inclined wall portion is spaced above the inner end of the next succeeding portion 30 whereby a plurality of expansion chambers, each having an opening as indicated at 3|, are provided, which discharge outwardly from the center of the furnace. Thus preheated air entering the conduit 28 at the inner end thereof may expand freely as it travels outwardly toward the outer end of the conduit 28, part of the air being discharged into the combustion chamber at the front, making contact with the gases therein at the discharge end of each expanded portion of the conduit.

At its outer or inlet end the conduit 20 is provided with a thermostatically controlled damper 32 such as more fully described in my copending application, Serial No. 216,498, filed June 29-, 1938, now matured into Patent No. 2,200,248 dated May 14, 1940. Briefly, this damper comprises a plate 33 having a plurality of circumferentially spaced openings and a damper plate 34 having openings arranged so as to pass into registry with the openings of the plate 33 when the damper plate 34 is rotated to different positions and to pass out of regist y with the openings in the plate 33 and block the passages therethrough in other rotated positions of the damper plate 34. The damper plate 34 is rotated to different positions by a bi-metal coil 35 which is responsive to changes in temperature within the furnace and increases and reduces the amount of air admitted through the duct 20 in a predetermined relation to the heat of the furnace. The damper thus described may be substituted for the usual closure door provided at the clean-out passage.

Within the duct 29 is a sleeve 36 which is open at its outer end adjacent the damper and which, at its inner end, opens upwardly so that some of the air admitted by the damper passes through the sleeve 36 and thus moderates the heat to which the bi-metal coil 35 is subjected.

At the inner end of the duct 20 is a downwardly facing opening 41: adjacent which are a series of radial notches 4|. The upper end of the preheating bell 2| is arranged to lit the bottom wall of the duct at the opening 49, said bell having a plurality of lugs 43, arranged to pass through the notches 4| in one turned position of the bell, and to become offset from the notches and locked in place in another turned position. If desired, cam surfaces may be provided at the under side of the lugs 43 and around the margins of the opening 49 so as to draw the preheating bell tightly against the under wall of the duct 29.

The preheating hell 2| has an upper portion 45 which slopes outwardly and downwardly, and a lower portion 45, which is somewhat globular and slopes inwardly and terminates in a restricted orifice 47. On the lower end of the bell 2| adjacent the orifice 41 is an outwardly flaring discharge nozzle 48 which slopes outwardly and downwardly, preferably at an angle of about 45 degrees so that the air discharged through the orifice 41 is guided outwardly toward the side walls of the furnace combustion chamber 3. A

plurality of radiating ribs 49 are provided on the inner wall of the preheating bell 2| so as to effect more rapid transmission of heat into air which passes into the bell. The entire duct 25 may be formed as an integral casting and the preheating bell 2| may also be formed as a separate integral casting.

Operatz'0n.-When the apparatus is installed in the furnace combustion chamber and the fire is started, it is apparent that the preheating bell 2| and the duct 20 are heated. When the furnace is relatively cool, the damper plate 34 is operated by the coil 35 to reduce the amount of air admitted through the duct 23 and thus cause the stack pull on the furnace to be effective in drawing air through the damper 6. As a result, the intensity of combustion of the under strata of the fuel bed is effected and gases are evolved rapidly. As the furnace becomes heated to a greater degree, the damper 32 operates, because of the change of temperature, to admit additional air through the duct 20. This air passes through the lower conduit 21 wherein it is subjected to the heat of the radiating hood of the furnace so that it becomes preheated to a certain degree. The air continues flowing inwardly, as indicated by the arrows 59, until it strikes the portion 29 of the wall 26, whereupon it is deflected generally downwardly into the preheat-'- ing bell 2L Since this bell is exposed to the full intensityof the heat of the burning gases and is provided with radiating ribs, as indicated at 49, the air thus admitted and passed into the preheating bell 2| is rapidly preheated to a relatively high degree and consequently tends to expand within the bell. Due to the stack pull and to the expansion of the air, part of this air passes out of the orifice 41 at relatively high velocity and spreads outwardly and downwardly, as indicated by the arrows 5| (Fig. 2), through the discharge nozzle 48 onto the fuel bed. Another portion of this air passes upwardly through the opening 49 into the conduit 28 and therealong, as indicated by the arrows 52, a portion of it discharging at each of the openings 3|. Thus, primary combustion is effected by the air admitted through the damper 6 and ash pit 1, this primary combustion determining the rate of evolution of the gases. Secondary combustion is obtained immediately over the fuel bed due to the admission of air through the preheating bell 2|. A tertiary combustion is obtained in the radiating hood of the furnace, due to the admission of the preheated air from the openings 3|.

If the furnacewere not provided with the apparatus described, it is apparent that the admission of more air through the ash pit I for effecting combustion of the evolved gases would result in a greater rate of evolution of the gases.-

Consequently, regardless of the increased amount of air in the ash pit, the amount of gases evolved would'always lead and be in excess of the amount of air admitted for effecting their combustion. Thus the rate of evolution of the gases would always be in excess of the amount of air required for their combustion. With the present apparatus, however, additional air may be admitted into the combustion chamber without materially affecting the rate of evolution of the gases so that a more nearly balanced relation between the rate of evolution of the gases and the air supplied for their combustion can be'maintained. Since part only of the additional air is admitted radiating hood, there is no danger of chilling the upper surface of the fuel bed and thus reducing the rate of evolution of the gases. Finally, the unconsumed volatile matter which is not burned directly in the main body of the combustion chamber is thoroughly aerated by preheated air in the radiating hood and is burned in the hood where the radiation of the furnace is most eiiicient. In event that the furnace reaches too high a temperature and the damper 6 is closed, then the air admitted through the duct 29 will continue for a considerable period sufficient to burn the gases evolved by the highly incandescent state of fuel in the under strata of the fuel bed. Gradually, however, the combustion of the under strata will be reduced due to lack of sufficient air through the damper 5. Consequently, the air admitted through the duct 20 will exhaust that required for combustion and will tend to reduce the temperature in the upper portion of the furnace. As the furnace gradually cools, the damper 32 will gradually close and reduce the amount of air in the proper relation of the rate of evolution of the gases. While the furnace is thus closed down or operating at a very reduced rate, gases entering the preheating bell 2| cannot accumulate therein but pass upwardly into the conduit 28 and thus discharge into the radiating hood. As a result, all danger of explosion, due to accumulating gases, is eliminated.

Referring further to the shape of the flange 48 which forms a flaring discharge for preheated air at t -e bottom of the bell .ZI the principal purpose of the 45 inclination of the flange is to enable stack pull to cooperate with the expanding heated air discharged from the orifice 41 in distributing the air uniformly over the fuel bed. Without such flange, the tendency is for the downwardly discharged air, in effect, to bore a hole in the fuel bed by impingement over a small region directly below the outlet. Natural expansion of the downwardly discharged column of air has been found insufficient so to distribute the air over the fuel bed, but by so fashioning the device that the ultimate outlet is increased greatly in cross pull can then become effective at in spreading the preheated air. of stack pull in cooperation with a definite level The element the expansion duct portion 28 effecting a suction or siphoning action on the lower conduit portion 21, Air drawn into the duct 21, being relatively cool, naturally tends to fall into the bell, and the heated air which rises into the duct 28 does not to flow but, due principally to stack pull on the preheated air through the outlet passages 3 5, augments it.

I claim:

1. An apparatus for the purposes described comprising an elongated duct having an upper conduit portion and a lower conduit portion, said portions being uncommunicated with each other between their ends, said lower conduit portion having an inlet at one end and a discharge opening at the other end, a hollow preheating bell at the discharge end of the lower conduit portion and arranged to receive air admitted through said lower conduit portion, the upper conduit portion having an inlet end in communication with the bell adjacent the discharge end of the lower conduit portion for receiving part of the air discharged from the lower conduit portion, said upper conduit portion having a discharge opening spaced from the discharge opening of the inlet oppose such tendency conduit portion, and said bell having a discharge opening spaced from and below said conduit.

2. In a furnace means for conducting air from outside the furnace and discharging the same into the furnace, a heating bell communicating with the discharge portion of said means, said bell having its axis disposed vertically and being of gradually increasing cross section downwardly for the major portion of its length, radiating fins on the interior of the bell arranged to convey the heat absorbed by the outer wall of the bell to air passing into the bell, and a downwardly facing restricted outlet opening in the bell arranged for admitting a portion of air which is preheated by the bell to an upper region of the fuel bed of the furnace, and means for admitting another portion of the air from the first means into the furnace above the level of the said outlet opening of the bell.

3. Apparatus for discharging preheated air in a furnace adapted to burn carbonaceous fuel,

chambers provided at the upper of the conduit 20 is important in comprising a generally horizontally extending conduit arranged adjacent an upper region of such furnace, said conduit having relatively offset and inclined upper walls which form outlets for the preheated air between them, a partition Wall in the conduit and dividing it into upper and lower conduit portions which are uncommunicated between their ends, said lower conduit portion having atone end an inlet opening adapted for communication with air outside of the furnace and having a discharge opening at the other end, said upper conduit portion having a single inlet opening and which inlet opening is adjacent the discharge opening of the lower conduit portion, aheating bell in communication internally with the discharge opening of the lower conduit portion and the inlet opening of the upper conduit portion and extending downwardly from the level of said conduit, and said bell having a discharge opening spaced below said conduit.

4. An apparatus for the purposes described comprising a conduit for air adapted to be mounted within a furnace and open to the exterior of the furnace, means longitudinally dividing said conduit in a manner to form separate passageways for air traveling in opposite directions, a damper at the inlet of' one passageway, a thermostat for controlling the damper and a housing for the thermostat leading through the dividing means and being open at one end for admitting outside air thereinto and being open at its other end.

5. An apparatus for the purpose described comprising a conduit adapted to be disposed approximately horizontally in a furnace with its outer end communicating with air outside the furnace, a horizontal partition longitudinally dividing the conduit, a preheating bell at the inner end of the conduit, said bell having openings at the top and bottom respectively for upward and downward discharge of expanded air into the furnace, the partition of the conduit at the inner end being inclined downwardly in a manner to direct air conveyed by the lower portion of the conduit downwardly toward the bottom of the bell.

6. An apparatus for the purposes described comprising a pair of elongated conduits, said conduits being uncommunicated with each other between their ends, one of said conduits having a free air inlet at one end and a discharge opening at the other end, a hollow preheating bell at the discharge end of the said one conduit, means as sociated with said discharge opening and arranged to direct air therefrom into the interior of the bell, the said other conduit having an inlet end arranged adjacent the discharge end of the said one conduit for receiving part of the air discharged from said discharge opening and the said other conduit having a discharge opening spaced from the discharge opening of the said one conduit and said bell having a discharge opening spaced from said conduits.

'7. In a furnace, conduit means to conduct air from outside of the furnace thereinto, a hollow heating means located inside the furnace and generally below the level of said conduit means and directly exposed to the heat of the fuel bed and having its interior connected at its upper por- 

